/Engine/Source/Runtime/Core/Public/Misc/MapErrors.h
Static Mesh {Static Mesh Actor} : Static mesh actor has NULL StaticMesh property: This warning is caused when there is a static mesh actor in a level with a NULL StaticMesh property. This can be a problem because the actor exists and is using memory, but doesn't have a static mesh to actually draw. This warning is usually the result of creating a StaticMesh actor without first selecting a StaticMesh in the generic browser. This warning can be fixed by first selecting a static mesh in the generic browser and then going to the StaticMesh actor's Property Window->StaticMeshActor Category->StaticMeshComponent->StaticMeshComponent Category to set the 'StaticMesh' Property.
static [FLazyName](API\Runtime\Core\UObject\FLazyName) StaticMeshNull;